A motor vehicle exposes a handling performance that is dependent on the extent and manner in which the vehicle is loaded with cargo. Cargo includes any kind of mass the vehicle transports, such as passengers, animals, solid items or an amount of liquid. Cargo influences the vehicle behaviour especially during phases of accelerating, braking and travelling along a curved path.
In addition to the influence of the extra mass of the cargo, the position of the cargo with respect to the vehicle may also impact the vehicle's handling performance. For instance, a vehicle that bears more load on its right-hand side may be inclined to turn more easily to this side but show difficulties turning to the other hand side. A cargo that is positioned near a driven axle may help preventing the driven wheels to skid during driveaway; placed close to a steering axle, the cargo may decrease the steerability of the vehicle.
While the effect of cargo on a vehicle's handling performance may be small in a passenger car, it can be considerable in a truck or bus because there is more opportunity to place a cargo in different positions in a cargo bay or cabin. Moreover, the weight of the cargo may easily exceed the weight of an unloaded truck.
Even careful initial loading sometimes does not prevent a situation of imbalance to occur, for instance if later on a part of the cargo is removed, while another part remains on the vehicle. Such imbalance may cause lopsided deterioration e.g. of tires and alter the vehicle's handling performance especially under critical conditions like sharp turning or hard braking, so that a driver may be unable to fully anticipate the vehicle's handling performance. Besides, the imbalance may lead to increased gasoline consumption due to an increased drag of those tires that are overly loaded.
If cargo is not sufficiently secured within the cargo bay, forces that act upon the vehicle and cargo while driving may cause the cargo to topple over, drop down or slidingly shift position. Of course, if a plurality of pieces of cargo is transported, a shifting may concern each transported piece in a different way and extent, and may change the balance of the vehicle in a complex fashion. Such dynamic changes may pass unnoticed by the driver and may therefore contribute to unpredictable and dangerous changes in the vehicle's handling performance.
With the advent of on-board electronic stability control systems, a number of techniques were developed that address the problem of vehicles with uneven load distribution, some of them attempting to compensate for the effects of cargo mass or cargo position on the vehicle by intervention into the suspension, propulsion, braking or steering system.
According to U.S. Pat. No. 6,313,742 B1, a method and apparatus for detecting compromised vehicle wheel and tire operating characteristics comprises detection of off-centre loads. To this end, sensor signals for rotational speeds of several vehicle wheels are evaluated. Both turns and imbalances may be detected through a side to side variation in wheel speeds. Turns are distinguished from imbalances by observing if the variation is only temporal.
U.S. Pat. No. 6,313,331 B1 proposes a method of monitoring the weight distribution on a vehicle and includes measuring characteristic values of axles, comparing them with expected values and potentially sending a warning signal to a driver of the vehicle.
U.S. Pat. No. 6,452,487 B1 discloses a technique for warning of a tip-over condition in a motor vehicle. Sensors on a left side and a right side of the vehicle pick up fractional cargo loads for the respective sides. Based on these values, a load ratio is determined that is compared with a threshold value and an alarm is raised on exceeding the threshold value.
DE 10 2004 060809 A1 discloses a method for determining an actual position of a centre of gravity of a motor vehicle based on spring travels on springs on at least one axle.
It is an object of the invention to provide a technique that quickly and reliably identifies shifted cargo on a moving vehicle.